<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

</body>

</html>

<script>

  // 解法一：toString
  let a = {
    value: 0,
    toString: function () {
      return ++this.value
    }
  }

  // 解法二：数据劫持
  // var i = 0
  // Object.defineProperty(window, 'a', {
  //   get() {
  //     return ++i;
  //   }
  // })

  if (a == 1 && a == 2 && a == 3) {
    console.log('判断成立');
  }
</script>